6-Acetyl-2,2-dimethyl-4-chromanone(6), isolated from Tussilago farfara LINN., was prepared by oxidation of 6-ethyl-2,2-dimethyl-4-chromanone(4) using chromium(VI) oxide in acetic anhydride and acetic acid.
The compound 4 was obtained, via the intermediate of ester 3, by condensation of p-ethylphenol and 3-methylcrotonic acid using diphosphorus pentaoxide in polyphsphoric acid.
The conversion of 3 to 4 also proceeds efficiently by stirring of the reaction mixture with glass globes in the absence of diphosphorus pentaoxide.